The Indian Ocean Dipole and Cholera Incidence in Bangladesh: A Time-Series Analysis

Abstract

BackgroundIt has been reported that the El Niño–Southern Oscillation (ENSO) influences the interannual variation of endemic cholera in Bangladesh. There is increased interest in the influence of the Indian Ocean dipole (IOD), a climate mode of coupled ocean–atmosphere variability, on regional ocean climate in the Bay of Bengal and on Indian monsoon rainfall.ObjectivesWe explored the relationship between the IOD and the number of cholera patients in Bangladesh, controlling for the effects of ENSO.MethodsTime-series regression was performed. Negative binomial models were used to estimate associations between the monthly number of hospital visits for cholera in Dhaka and Matlab (1993–2007) and the dipole mode index (DMI) controlling for ENSO index [NINO3, a measure of the average sea surface temperature (SST) in the Niño 3 region], seasonal, and interannual variations. Associations between cholera cases and SST and sea surface height (SSH) of the northern Bay of Bengal were also examined.ResultsA 0.1-unit increase in average DMI during the current month through 3 months before was associated with an increase in cholera incidence of 2.6% [(95% confidence interval (CI), 0.0–5.2; p = 0.05] in Dhaka and 6.9% (95% CI, 3.2–10.8; p < 0.01) in Matlab. Cholera incidence in Dhaka increased by 2.4% (95% CI, 0.0–5.0; p = 0.06) after a 0.1-unit decrease in DMI 4–7 months before. Hospital visits for cholera in both areas were positively associated with SST 0–3 months before, after adjusting for SSH (p < 0.01).ConclusionsThese findings suggest that both negative and positive dipole events are associated with an increased incidence of cholera in Bangladesh with varying time lags.

Climate and socioeconomic influences on interannual variability of cholera in Nigeria

“…Temperature is related to food contamination, which may consequently serve as a vehicle for cholera transmission (Rabbani and Greenough, 1999) depending on the physio-chemical properties of the contaminated food. Similarly, rainfall is well documented to have a positive relationship with cholera (Reyburn et al, 2011;Hashizume et al, 2011). The seasonal trend observed in the monthly hospital time series corresponds with the rainy season; this is consistent with what has been found in other regions (e.g.…”

Environmental Factors Influencing Epidemic Cholera

“…18 An increase in cholera outbreaks following heavy rainfall is observed in epidemic regions of Africa. 19 Similar observations have been reported in Bangladesh, [20][21][22] Haiti, 9 and East Africa. 23 The role of air temperature has also been highlighted in several recent studies.…”

“…Previous research in Kolkata and Dhaka have shown that precipitation is associated with an increase in cholera cases most likely caused by the feeding of nutrient-rich runoff into water bodies and flooding of the water supply intended for human consumption with river water harboring V. cholerae. 14,21 DISCUSSION AND SUMMARY Cholera occurrence is characteristically different in epidemic and endemic regions. Epidemic cholera regions are located away from but within 25 miles of a major river system.…”

The Role of Temperature Inversions in the Generation of Seasonal and Interannual SST Variability in the Far Northern Bay of Bengal

“…Furthermore, the northern Bay of Bengal is surrounded by densely populated areas, and environmental fluctuations can have important impacts on society. For example, earlier studies demonstrated that SST off Bangladesh was associated with cholera incidence in Dhaka, the capital and largest city in Bangladesh (Lobitz et al 2000;Constatin de Magney et al 2008;Hashizume et al 2011).…”